In a statement released today the FDA warned that the use of the drug “may in rare instances cause prolonged and sometimes painful erections known as priapism.”

The FDA updated drug labels and patient Medication Guides to include information about the rare but serious risk of priapism. If not treated right away, priapism can lead to permanent damage to the penis.

According to the FDA, priapism can occur in males of any ageand happens when blood in the penis becomes trapped, leading to an abnormally long-lasting and sometimes painful erection. Another ADHD drug, Strattera (atomoxetine), has also been associated with priapism in children, teens, and adults.

Priapism appears to be more common in patients taking atomoxetine than in those taking methylphenidate products; however, because of limitations in available information, the FDA does not know how often priapism occurs in patients taking either type of products.

Last year, Johnson & Johnson’s Janssen Pharmaceuticals paid approximately $181 million under a settlement and consent decree with 36 US states and the District of Columbia regarding previously disclosed allegations that it improperly promoted and marketed Risperdal to treat ADD and ADHD.

Risperdal is an antipsychotic drug used to treat mental disorders such as bipolar disorder and schizophrenia. Serious side-effects include gynecomastia, which causes male breast growth.